The present invention relates to an onboard treatment of ballast waters for ship units, which may contain potentially noxious and invasive living organisms, and in particular is directed to a method and a system for sterilizing ballast water by UV radiations, wherein, advantageously, the sterilisation can be carried out both with the ship unit stationary in a port and during the navigation.
The ballast waters are normally used by ship units during the transport both of goods and passengers, in order to balance their own cargo and optimise the stability conditions and floating of the same ship; generally, the ballast water is loaded into suitable storing tanks, positioned in the lower portion of the hull, according to variable balancing requirements of the ship. A standard ballasting procedure for a ship unit provides the loading of the ballast water when the ship is standing in a port, and successively unloading said ballast water, before or on arrival in a port or site different from the starting one, wherein the load conditions or the balancing requirements for the ship could be changed.
Consequently, it may happen that, native species and/or living micro-organisms of an ecosystem, withdrawn from a natural habitat of a starting port or site, can be unloaded in an arrival port or site, in a different ecosystem, generating potentially noxious conditions for the receiving environment. Invasive aquatic microorganisms are one of the most important problems involved in the use of ballast water on ships.
For this reason, regulations of the International Maritime Organisation (IMO) of the United Nations, directed to control and manage the ballast waters, impose the treatment of the ballast waters during charging in order to substantially eliminate the noxious living organisms, before said ballast waters are unloaded in a site or port different from the starting site or port, where the ballast waters have been loaded into the water storage tanks of a ship.